The present invention relates to an automatic transmission for a four-wheel drive vehicle provided with a transfer clutch for changing two-wheel driving into four-wheel driving.
Since the automatic transmission for a four-wheel drive vehicle is the same as that of the two-wheel drive vehicle in operation, it is desirable to use an automatic transmission designed for a two-wheel drive vehicle for constructing a transmission system for a four-wheel drive vehicle from an economical point of view. To meet such a requirement, it is necessary to easily convert the automatic transmission for the two-wheel drive vehicle to the automatic transmission for the four-wheel drive vehicle without changing the construction of the automatic transmission.
There has been proposed a four-wheel drive vehicle provided with a fluid operated clutch as a transfer clutch. In such a four-wheel drive vehicle, the fluid operated clutch is operated by pressure oil produced by an oil pump in the automatic transmission for operating the transmission. Accordingly, a pressure oil control system must be provided for operating the fluid operated clutch. In order to connect the pressure oil control system for the clutch to the pressure oil system in the automatic transmission with ease, the pressure oil control system should be designed into an independent system separated from the pressure oil system in the automatic transmission.